Liverpool's Champions League ambitions have been rocked by the news that Alisson will miss the first leg of their last-16 clash against Galatasaray. The Brazilian shot-stopper, who is still widely considered to be one of the world's top goalkeepers, was a notable absentee as the Reds confirmed their 21-man travelling squad for the daunting trip to Istanbul.Alisson took part in training on Monday but felt discomfort at the end of the session and will therefore not be risked. The timing is particularly tricky for head coach Arne Slot, who is looking to steer the Merseyside giants toward European glory in his second season. The Brazilian goalkeeper has made 32 appearances in all competitions this season and was in goal for their 3-1 win over Wolves in the FA Cup on Friday night. Slot will also be without Federico Chiesa, who missed Monday's session, thinning the attacking options available for the first-leg battle.In Alisson's absence, Giorgi Mamardashvili is set to be handed the gloves for the biggest game of his Liverpool career to date. The Georgia international, who arrived in a £25 million move from Valencia, has already registered 11 appearances during Alisson’s previous injury layoffs this season. Notably, one of those appearances came against Tuesday's opponents during the competition's league phase. Mamardashvili was thrust into the action in Istanbul earlier this term, replacing Alisson in the second half of a narrow 1-0 defeat.While Liverpool deal with injury woes, Galatasaray enter the tie brimming with confidence following a dramatic playoff victory over Juventus. However, the Turkish giants will have to navigate the return leg at Anfield without their vocal support after UEFA's Appeals Body confirmed a ticket ban for their fans following misconduct in Italy. For the first leg in Istanbul, however, the atmosphere will be as electric as ever as Okan Buruk’s men look to repeat their 1-0 victory over the Reds from earlier in the competition.Add GOAL.com as a preferred source on Google to see more of our reportingThe confirmed 21-man squad highlights a blend of experienced stars and emerging talent, though the lack of a senior backup for Mamardashvili is a concern. Freddie Woodman will step up from third choice to sit on the bench as Mamardashvili's understudy, with youngsters like Rio Ngumoha and Trey Nyoni also included in the travelling party. The Reds are still reeling from recent domestic inconsistency, including a defeat to Wolves in the Premier League, and the loss of Alisson only adds to the pressure on Slot’s tactical setup.